Additive manufacturing with nanofunctionalized precursors

Abstract

Some variations provide a process for additive manufacturing of a nanofunctionalized metal alloy, comprising: providing a nanofunctionalized metal precursor containing metals and grain-refining nanoparticles; exposing a first amount of the nanofunctionalized metal precursor to an energy source for melting the precursor, thereby generating a first melt layer; solidifying the first melt layer, thereby generating a first solid layer; and repeating many times to generate a plurality of solid layers in an additive-manufacturing build direction. The additively manufactured, nanofunctionalized metal alloy has a microstructure with equiaxed grains. Other variations provide an additively manufactured, nanofunctionalized metal alloy comprising metals selected from aluminum, iron, nickel, copper, titanium, magnesium, zinc, silicon, lithium, silver, chromium, manganese, vanadium, bismuth, gallium, or lead; and grain-refining nanoparticles selected from zirconium, tantalum, niobium, titanium, or oxides, nitrides, hydrides, carbides, or borides thereof, wherein the additively manufactured, nanofunctionalized metal alloy has a microstructure with equiaxed grains.

Description

PRIORITY DATA[0001]This patent application is a non-provisional application with priority to U.S. Provisional Patent Application No. 62 / 452,989, filed on Feb. 1, 2017, U.S. Provisional Patent Application No. 62 / 463,991, filed on Feb. 27, 2017, and U.S. Provisional Patent Application No. 62 / 463,952, filed on Feb. 27, 2017, each of which is hereby incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention generally relates to processes for additive manufacturing using functionalized precursors (e.g., powders), and additively manufacturing materials produced by these processes.BACKGROUND OF THE INVENTION[0003]Metal-based additive manufacturing, or three-dimensional (3D) printing, has applications in many industries, including the aerospace and automotive industries. Building up metal components layer-by-layer increases design freedom and manufacturing flexibility, thereby enabling complex geometries while eliminating traditional economy-of-scale constraints. In ...

AI Technical Summary

Benefits of technology

The patent describes a way to create metal alloy microstructures that are strong and free of cracks and porous voids. This is achieved by using a process called additive manufacturing, which involves layering metal powder to create a three-dimensional structure. The resulting microstructures have improved performance and can be used for various applications such as industrial components and medical devices.

Problems solved by technology

The vast majority of the more than 5,500 alloys in use today cannot be additively manufactured because the melting and solidification dynamics during the printing process lead to intolerable microstructures with large columnar grains and cracks.

3D-printable metal alloys are limited to those known to be easily weldable.

The limitations of the currently printable alloys, especially with respect to specific strength, fatigue life, and fracture toughness, have hindered metal-based additive manufacturing.

In contrast, most aluminum alloys used in automotive, aerospace, and consumer applications are wrought alloys of the 2000, 5000, 6000, or 7000 series, which can exhibit strengths exceeding 400 MPa and ductility of more than 10% but cannot currently be additively manufactured.

These same elements promote large solidification ranges, leading to hot tearing (cracking) during solidification—a problem that has been difficult to surmount for more than 100 years since the first age-hardenable alloy, duralumin, was developed.

This mechanism results in solute enrichment in the liquid near the solidifying interface, locally changing the equilibrium liquidus temperature and producing an unstable, undercooled condition.

As a result, there is a breakdown of the solid-liquid interface leading to cellular or dendritic grain growth with long channels of interdendritic liquid trapped between solidified regions.

As temperature and liquid volume fraction decrease, volumetric solidification shrinkage and thermal contraction in these channels produces cavities and hot tearing cracks which may span the entire length of the columnar grain and can propagate through additional intergranular regions.

Note that aluminum alloys Al 7075 and Al 6061 are highly susceptible to the formation of such cracks, due to a lack of processing paths to produce fine equiaxed grains.

Producing equiaxed structures requires large amounts of undercooling, which has thus far proven difficult in additive processes where high thermal gradients arise from rastering of a direct energy source in an arbitrary geometric pattern.

Scan strategies have been developed to control microstructure, but these strategies are highly material-limited and geometry-limited.

Use of nanoparticles in additive manufacturing has been described, but the nanoparticles are incorporated through ball milling, making scale-up and uniformity difficult.

Images